SYNOPSIS

DESCRIPTION

The
bridge
device bridges packets amongst Ethernet interfaces.
The number
b
in the bind is optional and selects a particular bridge
(default 0).

The
/net/bridge0
directory contains
ctl,cache,log,
and
stats
files, and numbered subdirectories for each physical interface.

Opening the
ctl
file reserves an interface.
The file descriptor returned from the
open(2)
will point to the control file,
ctl,
of the newly allocated interface.
Reading
ctl
returns a text string representing the number of the interface.
Writing
ctl
alters aspects of the interface.
The possible
ctl
messages are:

bind ether name ownhash path

Treat the device mounted at
path
(e.g.,
/net/ether0)
as an Ethernet medium
and associate it with this bridge (forward its packets to the
other interfaces associated with this bridge).
Ownhash
is an ‘owner hash’.

bind tunnel name ownhash path path2

Treat the device mounted at
path
as a network tunnel carrying Ethernet packets,
the device mounted at
path2
as an Ethernet
and associate them with this bridge
(forward its packets to the
other interfaces associated with this bridge).
Read packets from the
path
interface and write them to the
path2
interface.
Such tunnels have an MTU of 1400 bytes.

unbind type address [ownhash]

Disassociate the interface associated with
address
from this bridge.
Type
must be
ether
or
tunnel.

cacheflush

Clear the cache of (destination MAC address, port) tuples.

delay delay0 delayn

Set the
delay0
and
delayn
parameters.
delay0
is the constant microsecond delay per packet
and
delayn
is the microsecond delay per byte.

set option

Set bridge
option.
The only known option is
tcpmss,
which limits the TCP Maximum Segment Size of
TCP packets passing through to 1300 bytes.

clear option

Clear bridge
option.

Reading
stats
returns statistics about the bridge.

Reading the
log
file returns data from the bridge’s log
and will block at end of file awaiting new data.

Reading the
cache
file prints the cache of (destination MAC address, port) tuples,
one entry per line.
The format is:
the destination MAC (e.g., Ethernet) address in hex,
port number,
count of packets from this address,
count of packets to this address,
expiry time in seconds since the epoch,
and
e
for expired entries or
v
for valid entries.

In a connection subdirectory,
ctl
and
local
don’t do anything,
but
status
returns a one-line status summary.